1. Field of the Invention
The present invention relates to a sheet feeding device that pneumatically floats sheets to be picked up one by one from a sheet stack and fed into a transportation path, and the invention also relates to an image forming apparatus including the sheet feeding device.
2. Description of Related Art
A conventional sheet feeding device is described in, for example, Japanese Patent Laid-Open Publication No. 2010-254462. In the sheet feeding device described in Japanese Patent Laid-Open Publication No. 2010-254462, a stack of sheets (e.g., paper) is placed in a mounting portion of a feed tray or suchlike. The sheet feeding device blows air onto the stack of sheets from opposite sides, thereby separating and floating the top sheet. Simultaneously, air above the stack of sheets is sucked through a suction belt, so that the floated top sheet is attracted to the suction belt. The suction belt transports the attracted sheet to the transportation path, thereby feeding the sheet into the transportation path.
To adjust the amount of air to be blown onto the stack of sheets, the sheet feeding device uses an image pickup device to capture an image of the floated top sheet and the next sheet therebelow. Thereafter, edges of the sheets are detected from the captured image, and the gap between the sheets is calculated. Subsequently, the sheet feeding device adjusts the amount of air on the basis of the calculated gap.
However, the amount of light inside the sheet feeding device is insufficient for an image to be captured inside the sheet feeding device. Therefore, in some cases, edge detection might not be performed accurately. Moreover, during edge detection, at least the top sheet is floated, often with the result that its edges flap up and down. Consequently, depending on the degree of illumination, edge detection might not be performed accurately. As such, conventional sheet feeding devices have difficulty in calculating the exact gap between sheets.